LeetCode-Implement Queue using Stacks

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Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

class MyQueue {
    
    LinkedList<Integer> stack1 = new LinkedList<Integer>();
    LinkedList<Integer> stack2 = new LinkedList<Integer>();
    
    // Push element x to the back of queue.
    public void push(int x) {
        stack1.push(x);
    }

    // Removes the element from in front of queue.
    public void pop() {
       if (stack2.isEmpty()) {
           while (!stack1.isEmpty()) {
               stack2.push(stack1.pop());
           }
       }
       stack2.pop();
    }

    // Get the front element.
    public int peek() {
    	if (stack2.isEmpty()) {
           while (!stack1.isEmpty()) {
               stack2.push(stack1.pop());
           }
       }
       return stack2.peek();
    }

    // Return whether the queue is empty.
    public boolean empty() {
        return stack1.isEmpty() && stack2.isEmpty();
    }
}

LeetCode-Implement Queue using Stacks

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原文地址：http://blog.csdn.net/my_jobs/article/details/47617673